Polishing of materials to a high degree of smoothness is required in various industrial processes, including the manufacture of silicon semiconductor components or disks to be coated with magnetic storage media for the digital storage of information. Over the past several years, a significant increase in recording density in such thin-film media magnetic recording disks has been achieved, and there is a continuing effort to increase recording density further. High density storage capacity requires a thin, even magnetic coating and thus a minimal amount of topographical irregularity on the disk surface.
Another property important to achieving high recording density is low flying height, that is, a close proximity of the read/write heads to the disk surface. Such proximity decreases overlap of voltage signals in adjacent magnetic domains in the disk, thus permitting an increase in recording density and optimum read-write performance. To reduce flying height, and to improve wear resistance, it is desirable for the surface of the disk to be as smooth as possible, thus preventing contact of the disk surface with read/write heads during use.
A widely used type of polishing apparatus is that in which the substrate is placed between two rotating plates. For even polishing, a parallel, coaxial alignment of the plates should be maintained during operation. A persistent problem encountered in the use of such machines is oscillation of the polishing plates during operation. Such oscillation is typically caused by misalignment in plate supporting components or uneven pressure applied by drive mechanisms. In particular, side-to-side (radial) movement of one plate relative to the other produces both radial and angular misalignment, which results in uneven side-to-side polishing and also reduces the life of the polishing surfaces. If such misalignment is extreme or persistent, the machine must be readjusted, leading to downtime and losses in productivity.
It is therefore desirable to provide a polishing apparatus in which the polishing plates are maintained, preferably over an extended period of time, in substantially constant parallel and coaxial alignment. Ideally, any necessary correction of misalignment in the apparatus is isolated from the polishing plates.